What mechanical component did Leonardo da Vinci sketch in an early form?

Leonardo da Vinci sketched an early form of a ball bearing.

Around 1498, Leonardo made drawings showing balls placed between two rings. The arrangement was intended to reduce friction by allowing rolling contact instead of direct sliding contact between surfaces.

This idea resembles the principle used by modern ball bearings, which support rotating shafts and reduce friction in machines. Leonardo's sketch is important as an early recorded study of the concept, but it was not a standardized industrial bearing and did not by itself create the modern bearing industry.

A common mistake is to credit Leonardo with inventing every later bearing technology. Bearings existed in simpler forms before him, and modern bearings required later advances in materials, precision manufacturing, lubrication, and sealing.